1. Field of Invention
The present invention relates to the technical field of active-matrix driving electro-optical devices, and more particularly to the technical field of electro-optical devices including, in a laminate structure of a substrate, a capacitive electrode and a capacitive line for adding a capacitor to a pixel electrode, and a thin-film transistor (TFT) for switching a pixel.
2. Description of Related Art
Currently, in a TFT-driven active-matrix electro-optical device, when a TFT is supplied at the gate thereof with a scanning signal through a scanning line, the TFT is turned on, thereby supplying a pixel electrode through a source and a drain of the TFT with an image signal that is provided through a data line to a source region of a semiconductor layer. Since the image signal is supplied to each pixel electrode through each TFT for an extremely short period of time, a storage capacitor is typically added to each pixel electrode (in parallel with a capacitor of a liquid crystal) to hold the voltage of the image signal supplied through the TFT for a period of time substantially longer than the time of the on state of the TFT.
The storage capacitor is typically formed of a capacitive electrode that is at a pixel-electrode potential and is extended from a conductive polysilicon layer forming the drain region of the TFT connected to the pixel electrode, a dielectric layer, and a capacitive line being at a predetermined potential and including an electrode portion that is opposed to the capacitive electrode with the dielectric layer interposed therebetween. The capacitive line is fabricated of the same conductive layer as that forming the scanning line (a conductive polysilicon layer, for example), and is typically arranged laterally to run in parallel with the scanning line.
There is generally a strong market demand for a higher-definition display image in electro-optical devices. To achieve higher definition, the pixel pitch can be made finer while the aperture ratio of the pixel is increased (i.e., an aperture area of the pixel through which image light is transmitted is expanded with respect to a non-aperture area of each pixel through which no image light is transmitted).
In accordance with the above-mentioned conventional art in which the scanning lines and the data lines are respectively juxtaposed in an image display area, the non-aperture area of each pixel where the scanning line and the capacitive line are arranged becomes narrower as the aperture ratio of the fine-pitched pixel increases. As the pixel pitch becomes finer, it becomes more difficult to embed a capacitor having a sufficiently larger capacitance and to impart sufficiently higher conductivity to the scanning line and the capacitive line. When a capacitor having a sufficiently large capacitance is not available or a scanning line and a capacitive line having a sufficient conductivity is not produced, the electro-optical device suffers from cross-talk or ghosting in an image display thereof, thereby degrading the image quality. As the aperture ratio of the fine-pitched pixels increases, the degradation of image quality becomes more pronounced. In other words, an attempt to improve image quality creates another problem that is difficult to resolve.
In comparison with the problem, the present invention has been developed, and it is an object of the present invention to provide an electro-optical device which increases the pixel aperture ratio while increasing the capacitance of a storage capacitor (or controlling a reduction in the capacitance of the storage capacitor), and providing a high-quality image display free from cross-talk and ghosting.
To achieve the above object, the electro-optical device of the present invention can include, on a substrate, scanning lines and data lines that intersect each other, thin-film transistors, each connected to one of the scanning lines and one of the data lines, and pixel electrodes respectively connected to the thin-film transistors. The present invention can also include a storage capacitor laminated above each of the scanning lines and including a pixel-potential capacitive electrode connected to the pixel electrode and being at a pixel-electrode potential, a fixed-potential capacitive electrode at a predetermined potential, and a dielectric layer interposed between the pixel-potential capacitive electrode and the fixed-potential capacitive electrode.
In accordance with the electro-optical device of the present invention, the storage capacitor can be laminated on the scanning line (with an interlayer insulator interposed therebetween, for example), and can includes the pixel-potential capacitive electrode connected to the pixel electrode and being at the pixel-electrode potential, the fixed-potential capacitive electrode at the predetermined potential, and the dielectric layer interposed between the pixel-potential capacitive electrode and the fixed-potential capacitive electrode. The storage capacitor is thus produced in a region overlapping the scanning line on the substrate in a plan view by making use of the pixel-potential capacitive electrode formed in the region overlapping the scanning line and the fixed-potential capacitive electrode opposed to the pixel-potential capacitive electrode. Unlike in the conventional art, the fixed-potential capacitive electrode (or the capacitive line) is not arranged laterally in parallel with the scanning line, and the use of the scanning line and the fixed-potential capacitive electrode (or the capacitive line) does not expand the non-aperture area of each pixel, because the scanning line and the fixed-potential capacitive electrode do not run alongside and in parallel with each other. In other words, by forming the fixed-potential capacitive electrode (or the capacitive line) overlapping the scanning line on the substrate, the aperture area of each pixel is expanded while a formation area of the fixed-potential capacitive electrode (or the capacitive line) is expanded at the same time. The capacitance of the storage capacitor is thus relatively increased. A sufficiently wide line width is achieved, thereby imparting sufficient conductivity to the scanning line and the fixed-potential capacitive electrode (or the capacitive line). As a result, the electro-optical device has a high aperture ratio of the fine-pitched pixel while providing an improved image quality for a presented image free from cross-talk and ghost.
In one embodiment of the electro-optical device of the present invention, the thin-film transistor can include a gate electrode formed of part of the scanning line and located over the channel region thereof. This embodiment provides a so-called top gate thin-film transistor which includes the scanning line having a storage capacitor laminated thereon on the substrate.
In another embodiment of the electro-optical device of the present invention, the thin-film transistor includes a gate electrode formed of part of the scanning line and located below the channel region thereof. This embodiment provides a so-called bottom gate thin-film transistor which includes the scanning line having a storage capacitor laminated thereon on the substrate.
In yet another embodiment of the electro-optical device of the present invention, the gate electrode of the thin-film transistor can be formed of the same conductive layer as the conductive layer forming the scanning line. In accordance with this embodiment, a portion of the scanning line running in a linear or comb-like configuration and fabricated of a conductive polysilicon layer, a metal layer or an alloy layer is over the gate insulator of each thin-film transistor and functions as a gate electrode.
In yet another embodiment of the electro-optical device of the present invention, the gate electrode of the thin-film transistor can be formed of a conductive layer different from the conductive layer forming the scanning line. In accordance with this embodiment, an island gate electrode connected directly or via a contact hole to a linear scanning line fabricated of a conductive polysilicon layer, a metal layer or an alloy layer is arranged on the gate insulator of each thin-film transistor. The material of the gate electrode is a conductive polysilicon layer, a metal layer, or an alloy layer.
In still another embodiment of the electro-optical device of the present invention, the storage capacitor is located over the scanning line on the substrate. In accordance with this embodiment, a formation area of the storage capacitor is expanded making use of a non-aperture area overlapping the scanning line.
In still another embodiment of the electro-optical device of the present invention, the storage capacitor is located below the scanning line on the substrate. In accordance with this embodiment, a formation area of the storage capacitor is expanded making use of a non-aperture area underlapping the scanning line.
In still another embodiment of the electro-optical device of the present invention, the storage capacitor is located in an interlayer position over the data line on the substrate. In accordance with this embodiment, the storage capacitor is located in the interlayer position over the data line on the substrate, and a formation area of the storage capacitor is expanded by making use of a non-aperture area overlapping the scanning line.
In still another embodiment of the electro-optical device of the present invention, the storage capacitor is located in an interlayer position between the data line and the scanning line on the substrate. In accordance with this embodiment, the storage capacitor is located in the interlayer position between the data line and the scanning line on the substrate, and a formation area of the storage capacitor is expanded by making use of a non-aperture area overlapping the scanning line.
In still another embodiment of the electro-optical device of the present invention, one of the fixed-potential capacitive electrode and the pixel-potential capacitive electrode is formed of the same conductive layer as the conductive layer forming the data line. In accordance with this embodiment, the storage capacitor having the capacitive electrode fabricated of the same conductive layer as the conductive layer forming the data line, for example, fabricated of Al (aluminum), is produced in a non-aperture area overlapping the scanning line.
In still another embodiment of the electro-optical device of the present invention, the pixel-potential capacitive electrode is located over the fixed-potential capacitive electrode. Since the pixel-potential capacitive electrode is located over the fixed-potential capacitive electrode in accordance with this embodiment, one of the pixel electrode and the thin-film transistor is electrically connected to the pixel-potential capacitive electrode via a contact hole in a relatively easy manner.
In still another embodiment of the electro-optical device of the present invention, the pixel-potential capacitive electrode can be located below the fixed-potential capacitive electrode. Since the pixel-potential capacitive electrode is located below the fixed-potential capacitive electrode in accordance with this embodiment, the other of the pixel electrode and the thin-film transistor is electrically connected to the pixel-potential capacitive electrode via a contact hole in a relatively easy manner.
In still another embodiment of the electro-optical device of the present invention, the interlayer position of the pixel electrode is located over the scanning line on the substrate. In accordance with this embodiment, the pixel electrode arranged in the vicinity of a top layer in the laminate structure on the substrate is controlled by a thin-film transistor embedded in a layer therebeneath in a switching operation.
In still another embodiment of the electro-optical device of the present invention, the interlayer position of the pixel electrode can be located below the scanning line on the substrate. In accordance with this embodiment, the pixel electrode arranged in the vicinity of a bottom layer in the laminate structure on the substrate is controlled by a thin-film transistor embedded in a layer thereabove in a switching operation.
In still another embodiment of the electro-optical device of the present invention, the storage capacitor can be laminated with respect to not only the scanning line but also the data line. In accordance with this embodiment, the fixed-potential capacitive electrode (and the capacitive line) is laminated with respect to not only the scanning line but also the data line on the substrate, and the aperture area of each pixel is expanded while the formation area of the fixed-potential capacitive electrode (and the capacitive line) is enlarged. The capacitance of the storage capacitor is thus increased.
In still another embodiment, the electro-optical device of the present invention further includes a capacitive line which is connected to the fixed-potential capacitive electrode, is formed in a stripe configuration or a grid configuration and fixed to a predetermined potential outside an image display area.
In accordance with this embodiment, the fixed-potential capacitive electrode forming the storage capacitor in the image display area is fixed to the predetermined potential outside the image display area via the capacitive line running in a stripe configuration or a grid configuration on the substrate. The fixed-potential capacitive electrode arranged in the image display area is reliably and relatively easily connected to the predetermined potential by making use of a peripheral circuit surrounding the image display area or a constant-potential line or a constant-potential power source for a driving circuit.
In another embodiment, the capacitive line is formed of the same conductive layer as the conductive layer forming the fixed-potential capacitive electrode. In accordance with this embodiment, a portion of the capacitive line fabricated of a refractory metal or a polysilicon layer, for example, running and overlapping the scanning line, is located over the dielectric material forming each storage capacitor and functions as the fixed-potential capacitive electrode. In this embodiment, the capacitive line maybe formed of a conductive layer different from the conductive layer forming the fixed-potential capacitive electrode.
In accordance with this embodiment, an island fixed-potential capacitive electrode connected directly or via a contact hole to the capacitive line, fabricated of a refractory metal layer or polysilicon layer and running on and overlapping the scanning line, is arranged on the dielectric layer of the storage capacitor. The fixed-potential capacitive electrode is formed of a refractory metal layer or a polysilicon layer, for example.
In still another embodiment of the electro-optical device of the present invention, the pixel-potential capacitive electrode can be formed of an island conductive layer interposed between the thin-film transistor and the pixel electrode. In accordance with this embodiment, the pixel-potential capacitive electrode of an island conductive layer also functions as a conductive interlayer (or a barrier layer) that connects the thin-film transistor to the pixel electrode. In this embodiment, a junction of the island conductive layer with the thin-film transistor may be formed in a region corresponding to the data line, a junction of the island conductive layer with the pixel electrode may be formed in a region corresponding to the data line, and a junction of the island conductive layer with the pixel electrode may be formed in a region corresponding to the scanning line.
With this arrangement, the junction of the island conductive layer is located in the non-aperture area of each pixel overlapping the scanning line or the data line, and the junction does not narrow the aperture area of the pixel.
In another embodiment, the fixed-potential capacitive electrode is laminated between the scanning line and the pixel-potential capacitive electrode. In accordance with this embodiment, the fixed-potential capacitive electrode at the predetermined potential is laminated between the pixel-potential capacitive electrode at the pixel-electrode potential and the scanning line. Variations in the potential of the pixel-potential capacitive electrode do not adversely affect the scanning line through capacitive coupling (and conversely, variations in the potential of the scanning line do not adversely affect the pixel-potential capacitive electrode through capacitive coupling), and the adoption of the structure in which the storage capacitor is laminated on the scanning line reduces the degradation of image quality.
In still another embodiment of the electro-optical device of the present invention, the pixel-potential capacitive electrode can be laminated closer to the scanning line than the fixed-potential capacitive electrode is laminated to the scanning line. The pixel-potential capacitive electrode with the potential thereof varying with an image signal can be laminated closer to the scanning line in this arrangement. However, if the interlayer insulator interposed between the pixel-potential capacitive electrode and the scanning line is set to be thicker than a predetermined value, adverse interaction through capacitive coupling between the pixel-potential capacitive electrode and the scanning line is reduced in practice. The thickness of the interlayer insulator can be determined experimentally, based on experience, or by simulation so that the capacitive coupling is negligibly small in the specifications of the device.
The fixed-potential capacitive electrode may be separately formed of a conductive, transparent layer (polysilicon layer, for example) or may be formed of an embedded light shielding film (a refractory metal layer) for defining the aperture area of each pixel.
In still another embodiment of the electro-optical device of the present invention, the fixed-potential capacitive electrode can be laminated between the data line and the pixel-potential capacitive electrode. Since the fixed-potential capacitive electrode at the predetermined potential is laminated between the data line and the pixel-potential capacitive electrode at the pixel-electrode potential in accordance with this embodiment, variations in the potential of the pixel-potential capacitive electrode do not adversely affect the data line through capacitive coupling (and conversely, variations in the potential of the data line do not adversely affect the pixel-potential capacitive electrode through capacitive coupling), and the adoption of the structure in which the storage capacitor is laminated on the data line reduces the degradation of image quality. In this embodiment, the storage capacitor is formed not only in a region overlapping the scanning line but also a region overlapping the data line, and the capacitance of the storage capacitor is even further increased.
In still another embodiment of the electro-optical device of the present invention, the pixel-potential capacitive electrode can be laminated closer to the data line than the fixed-potential capacitive electrode is laminated to the data line. The pixel-potential capacitive electrode with the potential thereof varying with an image signal is laminated closer to the data line in this arrangement. However, if the interlayer insulator interposed between the pixel-potential capacitive electrode and the data line is set to be thicker than a predetermined value, adverse interaction through capacitive coupling between the pixel-potential capacitive electrode and the data line is reduced in practice. The thickness of the interlayer insulator is determined experimentally, based on experience, or by simulation so that the capacitive coupling is negligibly small in the specifications of the device.
In still another embodiment of the electro-optical device of the present invention, the fixed-potential capacitive electrode can include a portion, laminated between the scanning line and the pixel-potential capacitive electrode, in a region running along the scanning line on the substrate, and a portion, laminated between the data line and the pixel-potential capacitive electrode, in a region running along the data line on the substrate.
In accordance with this embodiment, the fixed-potential capacitive electrode at the predetermined potential can be laminated between the scanning line and the pixel-potential capacitive electrode in the region running along the scanning line on the substrate. In this region, therefore, an adverse effect through capacitive coupling between the scanning line and the pixel-potential capacitive electrode is reduced. Also, since the fixed-potential capacitive electrode at the predetermined potential is laminated between the data line and the pixel-potential capacitive electrode in the region running along the data line on the substrate, an adverse effect through capacitive coupling between the data line and the pixel-potential capacitive electrode is reduced in this region.
In yet another embodiment, in the region running along the scanning line, the pixel-potential capacitive electrode is formed of one of a first conductive layer and a second conductive layer that are laminated with the dielectric layer interposed therebetween while the fixed-potential capacitive electrode is formed of the other of the first and second conductive layers. In the region running along the data line, the pixel-potential capacitive electrode is formed of the other of the first and second conductive layers while the fixed-potential capacitive electrode is formed of the one of the first and second conductive layers.
In this arrangement, an adverse effect through capacitive coupling between the scanning line and the pixel-potential capacitive electrode is reduced in the region running along the scanning line while an adverse effect through capacitive coupling between the data line and the pixel-potential capacitive electrode is reduced in the region running along the data line.
In still another embodiment of the electro-optical device of the present invention, one of the pixel-potential capacitive electrode and the fixed-potential capacitive electrode is formed of a pair of electrodes that sandwiches the other of the pixel-potential capacitive electrode and the fixed-potential capacitive electrode from above and from below.
Since the one of the pixel-potential capacitive electrode and the fixed-potential capacitive electrode is formed of the pair of electrodes that sandwiches the other of the pixel-potential capacitive electrode and the fixed-potential capacitive electrode from above and from below in accordance with this embodiment, a storage capacitor having a larger capacitance is created with the area occupied on the substrate unchanged.
In this embodiment, the fixed-potential capacitive electrode can be formed of a pair of electrodes that sandwiches the pixel-potential capacitive electrode from above and from below.
Since the pixel-potential capacitive electrode at the pixel-electrode potential is sandwiched between the pair of electrodes forming the fixed-potential capacitive electrode from above and from below, variations in the potential of the pixel-potential capacitive electrode do not adversely affect the scanning line and the data line through capacitive coupling (and conversely, variations in the potential of the scanning line and the data line do not adversely affect the pixel-potential capacitive electrode through capacitive coupling), and the adoption of the structure in which the storage capacitor is laminated on the scanning line advantageously reduces the degradation of image quality.
In still another embodiment of the electro-optical device of the present invention, at least one of the pixel-potential capacitive electrode and the fixed-potential capacitive electrode can have a light shielding property. In accordance with this embodiment, the pixel-potential capacitive electrode and the fixed-potential capacitive electrode having the light shielding property are used to prevent light from entering the thin-film transistor or from traveling through the edge area of the aperture of each pixel.
In still another embodiment of the electro-optical device of the present invention, the one of the capacitive electrodes having the light shielding property contains a refractory metal. Specifically, the one of the capacitive electrodes is formed of a single metal layer, an alloy layer, a metal silicide layer, a polysilicide layer, or a multilayer of these layer, each layer fabricated of at least a refractory metal selected from the group consisting of Ti (titanium), Cr (chromium), W (tungsten), Ta (tantalum), Mo (molybdenum), and Pb (lead).
In yet another embodiment, the one of the capacitive electrodes having the light shielding property may be located over the thin-film transistor on the substrate, and may be formed of an upper light shielding film having conductivity and at least partly defining the aperture area of each pixel.
In this arrangement, the one of the fixed-potential capacitive electrode and the pixel-potential capacitive electrode is formed of the upper light shielding film having conductivity and defining the aperture area of each pixel (in other words, the embedded light shielding film arranged over the thin-film transistor has the function of the fixed-potential capacitive electrode or the pixel-potential capacitive electrode in addition to the originally intended light shielding property). This arrangement advantageously simplifies the laminate structure and the manufacturing process of the device in comparison with the case in which a dedicated conductive layer is added in a laminate structure to form a fixed-potential capacitive electrode or a pixel-potential capacitive electrode.
The upper light shielding film may be laminated between the conductive layer forming the scanning line and the conductive layer forming the data line, or may be laminated between the conductive layer forming the data line and the conductive layer forming the pixel electrode.
In this case, preferably, the scanning line, the data line, and the thin-film transistor do not extend beyond the formation area of the upper light shielding film on the substrate in a plan view.
In this arrangement, no light incident on the substrate is reflected from the scanning line, the data line and the thin-film transistor, because no portion of the scanning line, the data line and the thin-film transistor projects out of the formation area of the upper light shielding film. This arrangement efficiently precludes the generation of internal reflections and multiple reflections of light in the electro-optical device.
Preferably, the one of the capacitive electrodes having the light shielding property covers at least the channel region of the thin-film transistor.
Since the one of the fixed-potential capacitive electrode and the pixel-potential capacitive electrode having the light shielding property covers at least the channel region of the thin-film transistor in this arrangement, neither incident light nor returning light enters the channel region. This arrangement effectively controls the generation of photo-leakage currents arising from photoelectric effect, thereby preventing a change in transistor characteristics.
In this embodiment, the one of the capacitive electrodes having the light shielding property is located below the thin-film transistor on the substrate, and is formed of a conductive lower light shielding film covering at least the channel region on the substrate if viewed from the substrate.
In this arrangement, the one of the fixed-potential capacitive electrode and the pixel-potential capacitive electrode is formed of the lower light shielding film having conductivity at least covering the channel region of the thin-film transistor if viewed from the substrate (i.e., if viewed from the underside of the thin-film transistor) (in other words, the embedded light shielding film arranged under the thin-film transistor has the function of the fixed-potential capacitive electrode or the pixel-potential capacitive electrode in addition to the originally intended light shielding property). This arrangement advantageously simplifies the laminate structure and the manufacturing process of the device in comparison with the case in which a dedicated conductive layer is added in a laminate structure to form a fixed-potential capacitive electrode or a pixel-potential capacitive electrode.
The lower light shielding film may be deposited directly on the substrate or on an underlayer insulator formed on the substrate. In this case, preferably, the scanning line, the data line, and the thin-film transistor do not extend beyond the formation area of the lower light shielding film on the substrate in a plan view.
In this arrangement, light reflected from the rear surface of the electro-optical device or returning light passing through a light synthesizing system of a multi-panel projector composed of a plurality of electro-optical devices is not reflected from the scanning line, the data line and the thin-film transistor, because no portion of the scanning line, the data line and the thin-film transistor projects out of the formation area of the lower light shielding film. This arrangement efficiently precludes the generation of internal reflections and multiple reflections of light in the electro-optical device.
In still another embodiment of the present invention, the electro-optical device includes an upper light shielding film which is located over the thin-film transistor on the substrate and defines at least partly the aperture area of each pixel, and a lower light shielding film which is located below the thin-film layer on the substrate and covers at least the channel region of the thin-film transistor if viewed from the substrate, wherein the one of the capacitive electrodes having the light shielding property is formed of one of the upper light shielding film and the lower light shielding film, and wherein the lower light shielding film does not extend beyond the formation area of the upper light shielding film on the substrate in a plan view.
In this arrangement, the conductive upper light shielding film defining the aperture area of each pixel and the lower light shielding film covering at least the channel region of the thin-film transistor are further arranged. The one of the capacitive electrodes having the light shielding property is formed of one of the upper light shielding film and the lower light shielding film. This arrangement advantageously simplifies the laminate structure and the manufacturing process of the device in comparison with the case in which a dedicated conductive layer is added in a laminate structure to form a fixed-potential capacitive electrode or a pixel-potential capacitive electrode. Since a light beam incident on the substrate is reflected from the lower light shielding film projecting out of the formation region of the upper light shielding film, the generation of internal reflections and multiple reflections of light in the electro-optical device is effectively precluded.
In still another embodiment of the electro-optical device of the present invention, the pixel-potential capacitive electrode is formed of an extension of the conductive layer forming the drain region of the thin-film transistor. In accordance with this embodiment, the pixel-potential capacitive electrode is formed of the extension of the conductive layer (for example, a conductive polysilicon film) forming the drain region of the thin-film transistor. The pixel-potential capacitive electrode being at the pixel electrode potential connected to the drain region is relatively easily created.
In still another embodiment of the electro-optical device of the present invention, the pixel-potential capacitive electrode is formed of an extension of the conductive layer forming the pixel electrode. In accordance with this embodiment, the pixel-potential capacitive electrode can be formed of the extension of the conductive layer (for example, an ITO (Indium Tin Oxide) film) forming the pixel electrode. The pixel-potential capacitive electrode being at the pixel electrode potential is relatively easily created.
These and other operations and advantages of the present invention will become obvious from the following discussion of the embodiments.